Exchange coupled clusters of transition metal ions lie at the heart of all multi-electron catalytic events in biochemistry and are prevalent throughout redox biochemistry. The coupling strengths of exchange coupled dimers involving Fe, Mn or Ni in a variety of metalloproteins will be studied to accomplish the long range goal of understanding the structure and function of these clusters. The proteins to be studied include: (Fe-containing): hemerythrin, uteroferrin, ribonucleotide reductase and methane monooxygenase; (Ni-containing): urease and methyl-CoM reductase; (Mn-containing): pseudocatalase and Mn ribonucleotide reductase. Satura- tion magnetization data will be collected using a SQUID susceptometer and combined with EPR and Mossbauer studies of the self-same sample to yield complete description of the magnetic properties of these metalloproteins. Appropriate synthetic models will be studied as well. One specific goal will be to extend the range of the structurally informative exchange coupling parameter to include small values where the exchange coupling is less than the zero field splitting. * A second focus will be comparative saturation magnetization studies of metalloproteins having an active site with a single atom of either Fe or Mn. This will exploit the known similarities in the chemistry of Mn and Fe and serve as a check on the new saturation magnetization technique by comparison with Fe where Mossbauer spectroscopy can be applied. The aim is to develop saturation magnetization to measure the magnetic properties of manganese metalloproteins. Included in this project will be both Mn and Fe superoxide dismutases and Mn and Fe dioxygenases. Finally, the magnetic properties of metalloproteins containing more complex clusters including cytochrome c oxidase, sulfite and nitrite re- ductase, CO dehydrogenase, Ni hydrogenase, and nitrogenase will be inves- tigated. Saturation magnetization techniques in combination with EPR and Mossbauer spectroscopies will be developed to enable study of intermediate redox states, turnover complexes, and trapped reaction intermediates.